Process for manufacturing metal plane support for multi-layer lead frames

ABSTRACT

A process for manufacturing a metal plane support for making multi-layer lead frames adapted to be used for semiconductor devices. The lead frame support is made of a single thin metal strip having a plurality of lead frames continuously arranged in the longitudinal direction, the metal plane support is also made of a single thin metal strip and includes a plurality of metal planes, such as power supply planes, ground planes of the like, continuously arranged in the longitudinal direction corresponding to said plurality of lead frames. A pair of side rails are extending in the longitudinal direction for supporting the metal planes therebetween. The metal planes are connected to the rails via separating portions for removing the rails from the metal planes, after the metal planes are adhered to the corresponding lead frames.

This application is a continuation, of application Ser. No. 08/372,363,filed Jan. 13, 1995, now abandoned which is a CIP of Ser. No.08/095,516, filed Jul. 26, 1993 U.s. Pat. No. 5,410,180.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a metal plane support for making multi-layerlead frames adapted to be used for semiconductor devices. This inventionalso relates to a process for manufacturing multi-layer lead framesusing such a metal plane support.

2. Related Art

As shown in FIG. 9, a conventionally known multi-layer lead framecomprises a lead frame 2 and at least one metal plane, such as apower-supply plane 3, a ground plane 4, and the like, laminated by meansof electrically insulating layers 5a and 5b made of suitable resinmaterial, such as polyimide or the like. These electrically insulatinglayers 5 (5a and 5b) serve to electrically insulate the respectivelayers, i.e., the lead frame 2, the power-supply plane 3 and the groundplane 4, and also to adhere the respective layers together, thereby toform a unitary multi-layer lead frame.

Although the multi-layer lead frame shown in FIG. 9 has a structure ofthree layers, such a multi-layer lead frame may be a two-layer structurecomprising a single metal plane, i.e., a power-supply plane or a groundplane. Moreover, such a multi-layer lead frame may be a structure havingfour or more layers.

The power supply plane 3 and the ground plane 4 are electricallyconnected to power-supply leads and ground leads of the lead frame 2,respectively, and therefore maintained at predetermined voltages,respectively. In order to attain this, the power-supply plane 3 and theground plane 4 have extensions 6 and 7 protruding outwardly frompredetermined positions of the outer peripheries thereof. Thus, afterthe power-supply plane 3, the ground plane 4 and the lead frame 2 arelaminated together by the electrically insulating layers 5a and 5b,these extensions 6 and 7 are electrically connected to the power supplyleads and the ground leads of the lead frame 2, respectively, by spotwelding, laser beam welding, or the like.

Although FIG. 9 shows an example in which the second, intermediate layeris a power-supply plane 3 and the lowermost layer is a ground plane 4, amulti-layer lead frame in which the second layer is a ground plane andthe lowermost layer is a power-supply plane is also known in the priorart.

When manufacturing a multi-layer lead frame by laminating the powersupply plane and the ground plane onto the lead frame, as mentionedabove, the power-supply plane and the ground plane must be accuratelypositioned with respect to the lead frame. Also, these layers must befirmly adhered to each other while remaining insulated, and a reliableand effective manufacturing method must be attained.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a metal plane supportfor making multi-layer lead frames, in which a plurality of multi-layerlead frames continuously connected in the longitudinal direction caneffectively and accurately be manufactured.

Another object of the present invention is to provide a process formanufacturing multi-layer lead frames using such a metal plane support.

According to the present invention, there is provided a metal planesupport for making multi-layer lead frames adapted to be used forsemiconductor devices; a lead frame support made of a single thin metalstrip having a plurality of lead frames continuously arranged in thelongitudinal direction; said metal plane support being also made of asingle thin metal strip and comprising a plurality of metal planes, suchas power-supply planes, ground planes or the like, continuously arrangedin the longitudinal direction corresponding to said plurality of leadframes; a pair of side rails, extending in the longitudinal direction,for supporting said plurality of metal planes therebetween and means forconnecting said metal planes to said rails, said connecting meansincluding separating portions for removing said rails from said metalplanes, after said metal planes are adhered to said corresponding leadframes.

A process for making multi-layer lead frames using the above-mentionedmetal plane support and the lead frame support, comprises the steps ofadhering said metal plane support to said lead frame support by means ofan electrically insulating means, in such a manner that the respectivemetal planes are accurately positioned with respect to the respectivelead frames; and bending said side rails of the metal plane support toremove said side rails from said metal planes along said separatingportions.

It is advantageous that the width of said metal plane support is largerthan the width of said lead frame support, in such a manner that saidpair of side rails of said metal plane support protrude outwardly fromside edges of said lead frame support, when said metal planes areadhered to said corresponding lead frames, so that said side rails arebent by grippers for gripping said side rails.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view of an embodiment of a power supply plane support;

FIG. 2 is a plan view of an embodiment of a ground plane support;

FIG. 3 is plan view of an embodiment of a lead frame support;

FIG. 4 is an enlarged partial plan view of a separating portion of asupport bar;

FIG. 5 is an enlarged partial plan view of a separating portion of asection bar;

FIG. 6 is a plan view illustrating a laminated structure in which thepower-supply plane support and the ground plane support are adhered tothe lead frame support;

FIG. 7 is a partial cross-sectional view illustrating a laminatedstructure in which the power-supply plane support and the ground planesupport are adhered to the lead frame support;

FIG. 8 is a schematic illustration of an apparatus for separating theunnecessary parts from the multi-layer lead frame; and

FIG. 9 is a cross-sectional view of a multi-layer lead frame known inthe prior art.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to the accompanying drawings, some preferred embodimentsaccording to the present invention will be described in detail.

In FIGS. 1 and 2, metal plane supports for making multi-layer(three-layer) lead frames according to the present invention are shown,in which FIGS. 1 and 2 show a power-supply plane support and a groundplane support, respectively. The power supply plane support is made of asingle thin metal strip and comprises a pair of side rails 10a and 10bwhich support power supply planes 14 by means of support bars 12. Thepower-supply plane 14 defines a rectangular frame shape having arectangular central opening 14a. In the embodiment shown in FIG. 1, thepower-supply plane 14 is supported by the side rails 10a and 10b in sucha manner that each of the opposite edges of the outer periphery of thepower-supply plane 14, parallel to the side rails 10a and 10b ,respectively, is connected thereto by means of two associated andcorresponding support bars 12.

Although FIG. 1 illustrates only a single complete section or unit ofthe power-supply plane 14, as shown by the fragment of a successive suchsection at the right edge of the structure illustrated in FIG. 1, aplurality of power-supply planes 14 is supported by this power-supplyplane support structure in such a manner that plural power supply planes14 are continuously arranged in spaced relationship in a longitudinaldirection. Transverse section bars 18 are arranged between the two siderails 10a and 10b to connect them to each other, each thereof positionedbetween two adjacent power supply planes 14. The section bars 18 serveto increase the strength of the power-supply plane support structure soas to prevent deformation of the power supply plane support which makesit impossible to position the power-supply plane support accurately.

The above-mentioned guide rails 10a and 10b, the support bars 12 and thesection bars 18 are unnecessary in the final products and, therefore,they are removed after the power supply plane is adhered to the leadframe.

Therefore, the boundary portions between the support bars 12 and thepower supply plane 14 and between the section bars 18 and the side rails10a and 10b are provided with separating portions 20 and 22,respectively. The separation of the support bars 12 and the section bars18 can be effected by bending or folding the side rails 10a and 10babout the separating portions 20 and 22 as pivots. Thus, in order toeasily bend and separate the side rails 10a and 10b, the separatingportions 20 and 22 are provided with etched or cut grooves.

FIG. 4 is an enlarged partial plan view of the separating portion 20formed on the support bar 12. The separating portion 20 is formed as afine groove across the support bar 12 and, therefore, the thickness ofthis portion is reduced so as to easily separate thereat.

When separating the support bar 12 from the power supply plane 14, it isnecessary to prevent burrs from being formed at the outer periphery ofthe power-supply plane 14.

Such burrs might cause an electrical short circuit between planes, whenthe power-supply plane 14 is laminated to the other plane or planes. Inthis embodiment, therefore, as shown in FIG. 4, cut portions 24,indented toward the power supply plane 14, are formed at the positionswhere the support bar 12 is connected to the power supply plane 14.Also, the cut line, or grooves of the separating portion 20 forseparating the support bar 12 is made in conformity with the outerperipheral edge of the power supply plane 14.

FIG. 5 is an enlarged partial plane view of a separating portion 22 ofthe section bar 18. In the same manner as the separating portion 20 ofthe support bar 12, the separating portion 22 is formed by a fine groovealong a line across the section bar 18, but a slot or slots 26 areprovided along the fine groove. As the section bars 18 support thepower-supply plane support, the section bar 18 has a relatively largewidth compared ,to the support bar 12. Therefore, these slots 26 areformed for providing a reliable method of removing the relatively widesection bar 18 by bending or folding the guide rails 10a and 10b . Suchslots 26 can be formed by a known method, such as etching or the like.

The separating portions 20 and 22 of the support bars 12 and the sectionbars 18 may be provided as uncontinuous broken lines; moreover, it isnot always necessary to extend them to side edges of bars.

As the support bars 12 and the section bars 18 are removed as a whole bybending or folding the guide rails 10a and 10b about the separatingportions 20 and 22, respectively, the respective separating portions 20and 22 must be located on straight lines (i.e., in aligned relationshipwith each other, at the respective, opposite parallel peripheral edgesof the plane 14). Since the separating portions 20 of the support bars12 correspond to the outer, longitudinally extending peripheral edges ofthe power-supply plane 14 parallel to the side rails 10a, 10b, both theseparating portions 20 and 22 are located above straight linesrespectively corresponding to and parallel to the outer, longitudinallyperipheral edges of the power-supply plane 14.

As shown in FIG. 1, the power-supply plane 14 is provided with aplurality of through holes 16 for improving the sealing characteristicwith a sealing resin and connecting projections 17 which serve to makeelectrical connections between the power supply plane 14 and the leadframe. Also, an adhesive insulating tape is attached on the surface ofthe power supply plane 14 to adhere the same to the lead frame and toprovide electrical insulation therebetween.

The adhesive insulating tape has a square frame shape so that the entirearea of the power-supply plane 14 is covered by the adhesive insulatingtape, except the inner peripheral area of the power supply plane 14which is used as a wire-bonding area. Thus, the adhesive insulating tapeis attached on the surface of the power supply plane 14 after thepower-supply plane support is formed, by an etching or punching process,to a prescribed shape.

In the operation of adhering the adhesive insulating tape onto the powersupply plane, such a tape is supplied perpendicularly to thelongitudinal direction of the power supply plane support. In this case,in order to accurately position the adhesive insulating tape withrespect to the power-supply plane support, the side rails 10a and 10bare provided with positioning guide holes 28. The positions of the guideholes 28 on the side rails 10a and 10b are determined on the basis ofthe width of the adhesive tape, the width of the power supply plane 14,and the like, in such a manner that the adhesive insulating tape caneasily be fed perpendicularly to the longitudinal direction of the powersupply plane support.

The side rails 10a and 10b are also provided with guide holes 30 whichare used for positioning the power-supply plane support with respect tothe lead frame. The reference numeral 32 denotes an elongated hole whichis used for pressingly adhering the power supply plane support to thelead frame support.

FIG. 2 shows a ground plane support which is to be adhered to the bottomof the power-supply plane support shown in FIG. 1. The generalconstruction of the ground plane support is substantially the same asthat of the power supply plane support. Consequently, the ground planesupport comprises side rails 10a and 10b which support a ground plane 40by means of support bars 12. The side rails 10a and 10b are connected toeach other by means of section bars 18. The support bars 12 and thesection bars 18 are provided with separating portions 20 and 22,respectively, in the same manner as the power supply plane support, asmentioned above. The positions of these separating portions 20 and 22are similar to those of the power supply plane support.

The ground plane 40 has an outer peripheral size corresponding to thatof the power-supply plane 14 and is provided with connecting projections42 for electrically connecting the ground plane 40 to the lead frame.

As the ground plane 40 is adhered to and laminated on the power-supplyplane 14, an insulating adhesive tape is attached on a surface of theground plane 40 which the power-supply plane 14 faces. The adhesive tapehas a square frame shape corresponding to the shape of the power-supplyplane 14.

In the same manner as the power-supply plane support, theground-plane-support is provided with a plurality of guide holes 28 forpositioning the insulating adhesive tape, and guide holes 30 forpositioning the ground plane support, with respect to the lead framesupport.

These independent guide holes 28 and 30 serve to accurately position theadhesive tape with respect to each of the power supply support (FIG. 1)and the ground plane support (FIG. 2), and each of these power supplyand ground plane supports with respect to the lead frame support. Inthis case, an advantage can be obtained in that a common tape adheringapparatus or a common mold can be used, if the power supply plane 14 hasthe same size as the ground plane, even though the arrangement intervalof the power supply planes is different from that of the ground planes.

The separating portions 20 and 22 of the power-supply-plane-support orthe ground-plane support are provided on a surface thereof opposite tothe surface to which the adhesive tape is attached, i.e., the surface ofthe lead frame support to which another support is adhered. This isbecause an electrical short-circuit which might occur between the layerscan be prevented, even if burrs are formed when removing the side rails10a and 10b from the plane, after the lead-frame support, thepower-supply-plane support and the ground-plane support are laminatedtogether.

FIG. 3 shows an embodiment of the lead-frame support 49 with which thepower-supply-plane support and the ground-plane support are assembledand to which they are adhered. The lead-frame support comprises aplurality of lead frames continuously arranged in the longitudinaldirection (see fragment of further such support at right edge instructure illustrated in FIG. 3). The lead frame includes inner leads 50formed to enclose a semiconductor chip mount area and their outer leads52 supported by side rails 54a and 54b and transverse section bars 58.

The lead-frame support is provided with guide holes 30 for accuratelypositioning the power-supply-plane support and the ground-plane supportwith respect to the lead frame support.

The width of the lead frame support is smaller than that of thepower-supply-plane support and the ground-plane support. Therefore, therespective side rails 10a and 10b of the power-supply-plane support andthe ground-plane support protrude outwardly from the side edges of thelead frame support and, therefore, can easily be clamped (i.e., engaged,or gripped) for bending and removing the same, after the power supplyplane support and the ground plane support are laminated to thelead-frame support.

Using the above-mentioned lead frame support, power supply plane supportand ground plane support, a plurality of multi-layer lead frames can bemade by the following steps.

First, insulating adhesive tapes are initially attached to therespective ground planes and also insulating adhesive tapes areinitially attached to the respective power supply planes. Then, the leadframe support is positioned by inserting guide pins (not shown) intorespective and aligned guide holes 30 and 32 of the ground plane supportand the power supply plane support. The respective laminated frames,continuously arranged in the longitudinal direction, are pressedtogether by a suitable jig and heated to a predetermined temperature, sothat the respective ground planes 40 and power supply planes 14 arepressed together with, and adhered with respect to, the respective leadframes. After being pressed and adhered, the power-supply planes 14 andthe ground-planes 40 are completely fixed to the respective lead-framesand, if necessary, a curing process is added to this operation.

FIG. 6 shows a laminated structure in which the ground-plane support andthe power-supply-plane support are laminated to the lead-frame support.As can be clearly understood, the power-supply-planes 14 and theground-planes 40 are accurately positioned and adhered to the respectivelead frames. Since the width of each of the power-supply-plane supportand the ground-plane support is larger than that of the lead framesupport, the side rails 10a and 10b of the respective power supply planesupport and the ground plane support project outwardly from the sideedges of the lead frame support.

FIG. 7 shows the separating portions 20 of the power supply planesupport and the ground plane support, as so laminated to the lead framesupport 49. As mentioned above, since the respective separating portions20 and 22 are formed on the respective surfaces of the power supplyplane support and the ground plane support which are opposite to (i.e.,remote from) the lead in the assembled relationship; thereof as shown inFIG. 7, the separating portions 20 and 22 are located under (i.e., onthe lower surfaces of) the respective planes 14 and 40, in theorientation of FIG. 7.

Such a separating portion 20 may be a groove provided on the uppersurface of the respective plane adjacent to the lead-frame support 49,although in FIG. 7 the separating portion 20 is seen as a grooveprovided on the lower surface thereof opposite to the lead-frame support49. In addition, such separating portion 20 may be a pair of groovesprovided on both the upper and lower surfaces of the respective plane inopposite relation or in the vicinity of each other.

FIG. 8 shows a separating and removing apparatus. The laminatedstructure of the power supply plane support 14, the ground plane support40 and the lead frame support 49 is first clamped between an upper die64 and a lower die 66. The side rails 10a and 10b of the power supplyplane support and the ground plane support are then clamped by grippers70 and 71. Drive arms 74 (only one is seen in FIG. 8, but one or moreothers are provided and effectively hidden in FIG. 8 by the first suchdrive arm 74) are moved up and down several times by an air cylinder 82,in such a manner that the side rails 10a and 10b are bent or foldedseveral times, alternatively away from and toward the opposed side ofthe lead frame support and about the separating portions 20 and 22 bythe grippers 70 and as shown by doubled-headed arrows in FIGS. 7 and 8.It is preferable that a bending stroke of the grippers 70 is graduallyreduced, while a bending speed is gradually increased. Thus, the supportbars 12 and the section bars 18 are broken off, or released along theseparating portions 20 and 22, to permit removal thereof. The laminatedpower supply planes 14, the ground planes 40 and the lead frames remaingrasped, or clamped, by the upper and lower dies.

Although it is most preferable that the bending stroke of the grippers70 and 71 is gradually reduced and on the other hand the bending speedthereof is gradually increased, as mentioned above, it is also possiblethat the bending stroke and speed of the grippers 70 and 71 canappropriately be changed. For instance, the bending stroke of thegrippers 70 and 71 may be constant and on the other hand the bendingspeed may be is gradually increased. In another instance, the bendingstroke of the grippers 70 and 71 may be gradually increased and on theother hand the bending speed may gradually be reduced.

After the side rails 10a and 10b and the section bars 18 are removed,the connecting projections are electrically connected to predeterminedleads of the lead frame by a spot-welding, laser beam welding, or thelike, so that the power supply plane 14 and the ground plane 40 areelectrically connected to the lead frame. A multi-layer lead frame isthus obtained.

Although preferred embodiments and modifications of this invention havebeen described above with reference to the drawings, it should beunderstood that the scope of this invention is not limited to suchembodiments or modifications, and that other modifications can be madeby a person skilled in the art within the scope or spirit of thisinvention as claimed in the attached claims.

For example, in the above embodiment, although the frame widths of thepower supply plane support and the ground plane support are the same, itis also possible to make the ground-plane support wider than thepower-supply-plane support.

In the above embodiment, the widths of the power-supply-plane supportand the ground-plane support are larger than the width of the lead-framesupport, so that the side rails can easily be gripped and bent. However,the widths of the lead-frame support, the power-supply-plane support andthe ground-plane support may be the same, but the side edges of the leadframe support may be provided with recesses, so that the side rails canbe gripped through these recesses.

In the above embodiment, although the multi-layer lead frame has threelayers, the present invention can also be applied to a multi-layer leadframe having two layers or four or more layers. Also, an adhesive tapemay be attached beforehand to either of the respective opposed surfacesof two adjacent such layers which are to be adhered to each other.

We claim:
 1. A process for making a multi-layer lead frame forsemiconductor devices, comprising the steps of:a) preparing a lead-framesupport made of a single thin metal strip having a plurality of leadframes continuously arranged in a longitudinal direction, and includinga metal plane support made of a single thin metal strip and including aplurality of metal planes continuously arranged in the longitudinaldirection corresponding to the plurality of lead frames, a pair of siderails extending co-planar with the metal planes in the longitudinaldirection, for supporting the plurality of metal planes therebetween,first connectors between the metal planes and the side rails, and secondconnectors between the side rails and bars extending between the siderails, the first and second connectors including breakable portions; b)laminating the metal plane support to the lead frame support utilizinginsulating adhesive tapes; c) gripping the side rails; d) bending theside rails at the breakable portions within an arc including a firstgripping position co-planar with the metal planes and a second positionnon-planar with the metal planes to break the breakable portions; and e)removing the side rails from the metal planes and bars.
 2. The method asrecited in claim 1, wherein the metal plane support is prepared so thata width of the metal plane support is larger than a width of the leadframe support.
 3. The process as set forth in claim 1, wherein thegripping and bending steps use a gripper having a bending stroke and abending speed,wherein at least one of the bending stroke and the bendingspeed is changed during the bending step.
 4. The process as set forth inclaim 3, wherein the bending stroke is gradually reduced and the bendingspeed is gradually increased during the bending step.
 5. The process asset forth in claim 3, wherein the bending stroke is constant and thebending speed is gradually increased during the bending step.
 6. Theprocess as set forth in claim 3, wherein the bending stroke is graduallyincreased and the bending speed is gradually reduced during the bendingstep.